While plastic containers have found wide spread utility in packaging foods and non-food products, they have often been found to be lacking in their barrier characteristics towards gases such as oxygen and carbon dioxide, or solvents such as gasoline, toluene, methylene chloride, or moisture. The need for barrier properties towards oxygen, carbon dioxide, etc., is felt most importantly for the packaging of food. Oxidation of food due to the ambient oxygen could cause browning, rancidity, off-taste and off-smell, mold-formation, etc., sometimes posing serious health hazards. A less serious yet commercially important problem is the loss of carbon dioxide from carbonated beverages, causing the beverage to go "flat".
The need for barrier towards organic substances is felt in both the foods as well as non-food applications. While it is desirable to package a number of products, such as coffee or fruit juices in unbreakable, light weight or transparent plastic containers, such containers often absorb the essential oils and aroma components out of the product, resulting in an off-taste or smell, called distortion. The perfume, cologne, and cosmetic industry has also long recognized the same problem with respect to their packaging needs. The solvent barrier of a plastic container is also a very important characteristic when there is a need to package items like gasoline additives, solvent-based cleaners, etc. The industry has also long faced the problem of migration of unreacted monomers, low molecular weight polymers and other processing aids and additives from the container into the product; i.e., leaching.
Numerous attempts have been made to improve the barrier characteristics of plastic containers. For example, U.S. Pat. No. 3,862,284 discloses a process whereby the barrier properties of blow molded thermoplastic articles are improved by employing a blowing gas containing about 0.1 to about 20% by volume fluorine during the expansion of the parison.
U.S. Pat. No. 4,515,836 discloses a process for providing a substrate such as a polyethylene terephthalate container with a gas barrier coating of a copolymer of vinylidene chloride. The outside surface of the container is impacted with a stream of a stabilized aqueous polymer dispersion with sufficient force to cause selective destabilization of the dispersion at the surface interface to form a gel layer containing the polymer in the continuous phase. This gel layer serves as an adhesive layer for an overlaying layer of the aqueous polymer dispersion as a continuous uniform coating.
U.K. Pat. No. 2069870B discloses a process for improving the barrier properties of polymeric containers, by treating at least one surface of the container with sulphur trioxide, followed by washing with an aqueous medium and subsequently applying a layer of a dispersion of a melamine-formaldehyde or urea-folmaldehyde condensation product. The dispersion layer is then cured to form the final product.
U.S. Pat. No. 4,247,577 discloses a method for placing a covering layer of a cured organopolysiloxane composition onto the surface of a shaped article of a vinyl chloride resin in order to improve or mask defective surface properties of the resin. The method comprises treating the surface of a vinyl chloride resin article with a low temperature plasma of gas, placing a covering layer of a curable organopolysiloxane composition on the so treated surface of the article, and subjecting the article with the curable organopolysiloxane composition to curing conditions.
U.S. Pat. No. 4,550,043 discloses preforms formed by injection molding thermoplastic material which have internal barrier layers and internal layers of high thermal stability. The disclosed preforms are utilized in the forming of blow molded articles.
Dixon, et al., U.S. Pat. No. 4,009,304 teaches a process for improving adhesion of polyester yarn, tire cord or fabric in polyester reinforced rubber goods such as tires. Improved adhesion is achieved by fluorinating the polyester yarn, tire cord or fabric prior to incorporation into the tire and rubber goods.